A critical assessment of the superconducting pairing symmetry in NaxCoO2•yH2O
A critical assessment of the superconducting pairing symmetry in NaxCoO2•yH2O
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DOI：
10.1038/nphys126
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发表时间：
2005-11-01
期刊：
影响因子：
19.6
通讯作者：
Johannes, MD
中科院分区：
文献类型：
--
作者：
Mazin, II;Johannes, MD
Na（x）CoO（2）中心点yH（2）O必须水合才能超导（1），它的三角形CoO 2层与高温超导体的正方形CuO 2层形成了有趣的对比。它的超导性通常被认为是非常规的，因为库珀对不像传统超导体那样处于具有s波对称性的自旋单重态。根据泡利不相容原理，具有单重态（三重态）自旋部分的对具有对应的偶（奇）空间部分，根据对的角动量被指定为s-、p-、d-或f-波配对。然而，在Na（x）CoO（2）中心点yH（2）O中，实验报告经常是矛盾的（2-6），并且仍然缺乏任何特定配对状态的可靠证据。这导致了前所未有的配对对称性建议（2，3，5，7 -13）（可能是有史以来单个化合物的最大数量），每个都与可用数据的一些子集一致。在这里，我们测试了25个电子学允许的配对状态（14）中的每一个，以确定化合物的属性。令人惊讶的是，这消除了大多数可能的配对。剩下的两个态都具有f波对称性，这表明Na（x）CoO（2）中心点yH（2）O可能是迄今为止发现的最奇特的超导体。我们讨论这些国家的预期功能，并建议实验来区分它们。
Na(x)CoO(2)center dot yH(2)O must be hydrated to superconduct(1), and its triangular CoO2 layers provide an intriguing contrast with the square CuO2 layers of the high-temperature superconductors. Its superconductivity is often assumed to be unconventional in that the Cooper pairs are not in a spin singlet state with s-wave symmetry, as with conventional superconductors. According to the Pauli exclusion principle, pairs with a singlet (triplet) spin part have a corresponding even (odd) spatial part, designated as s-, p, d- or f-wave pairing in accordance with the pair angular momentum. However, in Na(x)CoO(2)center dot yH(2)O, experimental reports are often contradictory(2-6) and solid evidence for any particular pairing state remains lacking. This has led to an unprecedented number of proposals(2,3,5,7-13) for the pairing symmetry (perhaps the greatest number ever for a single compound), each in agreement with some subset of the available data. Here we test each of the 25 symmetry-allowed pairing states(14) against firmly established properties of the compound. Surprisingly, this eliminates most possible pairings. The two remaining states both have f -wave symmetry, suggesting that Na(x)CoO(2)center dot yH(2)O may be the most exotic superconductor discovered so far. We discuss expected features of these states and suggest experiments to distinguish between them.